Helicobacter pylori (Hp) is suspected to play a role in gastric carcinogenesis. A pilot study will assess the feasibility of conducting interventions designed to interrupt the transmission of Hp among children in a high prevalence population for the purpose of identifying the transmission route of this infectious agent. The interventions to be piloted are intended to discriminate between three plausible hypotheses regarding the transmission of Hp: I) direct person-to-person transmission; II) waterborne transmission; or III) a combination of direct person-to- person and waterborne transmission. The pilot will take in an Andean Colombian community. From 420 families who previously participated in a descriptive study of Hp transmission, 64 families with children previously determined to be infected with Hp will be selected for characteristics favoring excellent compliance with study interventions. An index child known to be Hp positive from each family will receive standard antibiotic treatment to clear Hp; at the same time, each family will be randomly assigned to one of four intervention groups: a) concurrent treatment of family members with triple therapy followed by bismuth; b) water purification regimen c) a and b; or d) treatment of index child only. Hp eradication will be verified in index children following anti-Hp therapy. The interventions will be closely supervised for four months. At the end of the intervention period, Hp status will be determined for the index children in order to compare reinfection rates across intervention groups. The main goals of the proposed pilot are the assessment of compliance with interventions relevant to two distinct infectious-agent transmission routes and the evaluation of the overall feasibility and value of implementing such interventions on a scale large enough to permit statistical discrimination between the three Hp transmission hypotheses in need of testing.